If you've watched any of the Planet Earth stuff on Discovery HD, the technical 'how to' programs that follow the main show are an interstitial, it's a mini program that fills up the time between the main programs. Sometimes if you watch IFC or Sundance at all, they might have a short film or a short animated flick that fills in the time between the longer movies.

thanks> excellent description> makes sense.. so it's not a form
of cutting, rather a programming method of going into segs,credits,breaks etc. with a "mini-program" to fill space or
a sidebar to main prorgram?

Well, you aren't cutting a half hour show, so yes. Interstitials can also be little vignettes between scenes of a show (like an awards show or something). Little scenes during costume changes, or when David Letterman appears to run around new York when really he's sitting back stage and runs in at the last minute.

Not exactly interstitials in the current sense, but an interesting gimmick I've seen. I think this was in the credits for Dharma & Greg, but the the producers would put up a flash frame of a whole page of tiny chyron for a split second in the credit roll. If you still-framed it at home, you would get to read some little essay or joke/story or something from the maker of the program aimed directly at the fan base of the show, not unlike a blog posting.

Lately, there are some 30 second spots from General Electric, within which they do kind of a similar thing: right near the end of the spot, before the final logo shot, they drop in five to eight frames of stills that tell an entire story, frame by frame. Almost like subliminal cuts. These only loosely have anything to do with the subject of the spot, but if you take the time to look thru them, they can be amusing. I find it to be an interesting tactic to get people to spend more time looking at your commercial. Sure, it's only people with OCD, but still...:-) I think it's a great gimmick to use if say, you're running a contest and the clues to winning are placed in this way.